The device has instructions not to install it within 10 meters of the electrical service panel. Why is that? Is there a corresponding maximum distance beyond which it should not be used?

The reasoning for the minimum installation distance of 10 meters is to better protect from transients. The closer you are to the service panel the higher the “transient power” [aka Surge] you may receive. The inductance and resistance of the wires at longer lengths reduce the amount of transient power that can transfer to any surge protection device.